spindle Documentation

Transcription

1 spindle Documentation Release Jorge Ortiz, Jason Liszka May 19, 2014

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5 spindle Documentation, Release Spindle is a library and code generation tool developed at Foursquare for representing data stored in MongoDB. It s based heavily on Apache Thrift, so understanding some Thrift fundamentals is important. However, most of Spindle is custom Scala code generation developed to work with Thrift models. Contents: Contents 1

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7 CHAPTER 1 Thrift Thrift is a framework that allows you to define serializable datatypes in a language-independent manner. These datatypes are described in.thrift files which conform to the Thrift Interface Description Language (IDL). The standard Thrift compiler will read Thrift IDLs and generate code for many different languages: Java, Python, JavaScript, C++, etc. We ve built a custom Thrift compiler (documented here) which generates Scala code. 1.1 Data Model Thrift s data model has the following base types: bool - true/false boolean value (Java s boolean) byte - 8-bit signed integer (Java s byte) i16-16-bit signed integer (Java s short) i32-32-bit signed integer (Java s int) i64-64-bit signed integer (Java s long) double - 64 bit IEEE 754 double precision floating point number (Java s double) string - UTF-8 encoded text string (Java s string) binary - sequence of unencoded bytes (Java s Array[Byte] or ByteBuffer) Thrift s data model includes an enum type (equivalent to Java s enum). On the wire, enums are represented as 32-bit integers. Thrift s data model also has the following parametrized container types. The parameters <a> and <b> can be primitives, enum s, or struct s. list<a> - ordered list of elements (Java s List<A>) set<a> - unordered list of unique elements (Java s Set<A>) map<a, b> - a map of unique keys to values (Java s Map<A, B>). Warning: non-string map keys will fail at runtime if you try to use TBSONObjectProtocol. Thrift includes three class types: struct - numbered fields, with a type and an optional default value union - tagged union types exception - like struct s, but can be used in the throws clause of a service 3

8 spindle Documentation, Release Finally, Thrift allows you to define constants and typedefs. A constant is a value of any Thrift type. A typedef is an alias of any Thrift type. 1.2 Interface Definition Language (IDL) Thrift data structures are described in.thrift files which conform to the Thrift IDL grammar. You can see the Thrift Tutorial for an example, or reference the formal grammar. 1.3 Serialization Formats There are four serialization formats we use. TBinaryProtocol - The original binary encoding included with Thrift. It is not well-documented, but is fairly simple. Field names are ommitted (only integer field identifiers are used), types are encoded as byte identifiers, sizes are prepended as integers. TCompactProtocol - A more compact binary encoding. Also not well-documented, but somewhat described here TReadableJSONProtocol - Reads and writes human-readable JSON. Unlike TJSONProtocol, ituses actual field names for keys, rather than field identifiers. If the field has a wire_name annotation, will use that instead of the name. Includes special handling for ObjectId. TBSONObjectProtocol - Reads and writes BSON DBObject s. It uses field names for keys. If the field has a wire_name annotation, will use that instead of the name. Includes special handling for ObjectId and DateTime. 4 Chapter 1. Thrift

9 CHAPTER 2 Records 2.1 Creating a Record There are three ways to create a Record apply method The easiest way to create a Record is to use the companion object s apply method. This method only works if you know the value of all of the Record s fields, even optional fields. This is useful for structs that have a small, usually fixed number of fields. (Note that if you add another field to your struct, any existing calls to apply will fail due to insufficient arguments.) Example (Thrift file): struct LatLong { 1: optional double lat 2: optional double long Example (Scala file): val ll = LatLong(40.65, ) Builder If you need to omit optional fields, or if you want to pass around a partially-constructed Record before you know all its fields, you will want to use a Builder. Builders are created using the newbuilder method on a Record s companion object. Fields on the builder are set using methods with the same name as the field. Field setter methods can be passed either a value or an Option value. To finish constructing a Builder, call result or resultmutable (returns a Record that conforms to the Mutable trait). Builders enforce that all required fields are set before result can be called. Example: val v = (Venue.newBuilder.id(new ObjectId()).venuename(Some("Foursquare HQ")).likeCount(None).result()) 5

10 spindle Documentation, Release Raw If for whatever reason a Builder is not flexible enough to do what you want, you can always instantiate a Raw class. You can use the createrawrecord method on the Record s companion object or you can call new directly on the Record s Raw class. This is unsafe, as it will not verify that required fields are set and can seriously corrupt data. Make sure you know what you re doing before you use Raw constructors. 2.2 Reading/Writing Records All records have read and write methods that take one argument: a TProtocol. We use a number of protocols, depending on the serialization format you want to read from or write to. See the section on Serialization Formats. Each protocol has a particular way in which it s constructed. Refer to the documentation for each protocol on how to use them. If you re reading in a record, it s acceptable to use the createrawrecord method on the MetaRecord companion object to instantiate a record that you can call read on. 2.3 Traits Every record has a trait of the same name that defines a mostly immutable interface to that record (the exception being some mutable methods for priming foreign keys). Methods that modify the record are generally only available as part of the Mutable trait Field Access The record s trait has a bunch of methods for field access. Not all of them are always available. Given a field named foo, the following field access methods may be available: foo - Returns the value of the field. Only available if a default is available (in which case it aliases fooordefault), or if the field is required (in which case it aliases fooorthrow). foooption - Returns an Option with the value of the field, or None if the field is not set. Always available. fooordefault - Returns the value of the field, or the default value if the field is not set. Only available if a default is available (either there s an explicit default in the.thrift file, or the field is a primitive or a collection, in which case the default is 0/0.0/false/empty/etc). fooornull - Returns the value of the field, or null if the field is not set. For primitives, typed to return the boxed type (e.g., java.lang.integer instead of scala.int) so that null is valid. In general, avoid using fooornull. Prefer foooption in general and fooorthrow if you want to fail fast (such as in tests, etc). Only use fooornull if you re writing performance-sensitive code that can t afford to allocate an Option. fooorthrow - Returns the value of the field, or throws an exception if the field is not set. fooisset - Returns true if the field is set, false otherwise Special Field Access Some field types have special access methods: foobytearray - if the field is of the binary thrift type, this method will exist and return an Array[Byte] (instead of the more efficient java.nio.bytebuffer) 6 Chapter 2. Records

11 spindle Documentation, Release foostruct - if the field has a bitfield_struct or bitfield_struct_no_setbits annotation, this method will exist and return a populated bitfield struct. (See: Bitfields) foofk - if the field is a foreign_key field, this method will exist and return the foreign object. (See: Priming) 2.4 Other Methods Other methods on the record trait: tostring - uses TReadableJSONProtocol to create a pretty-printed JSON string representation of the record hashcode - uses scala.util.murmurhash to produce a hash code from all the already-set fields on the record equals - compares two records to make sure that all their fields have the same set state, and if they re both set that they have the same value compare - compares two records by their set state for each field and their value for each field copy - similar to case class copy, creates a shallow copy of a record; has method arguments with default values so you can override the value of a single field or many fields when copying deepcopy - creates a deep copy of a record; doesn t take arguments mutablecopy - creates a shallow copy of a record, with the Mutable trait as its return type mutable - if the underlying implementation is mutable, return this typed as a Mutable trait, otherwise make a mutablecopy tobuilder - creates a new builder that has been initialized to have the same state as this record 2.5 Mutable Trait TODO: the Mutable trait interface is likely to change before being finalized 2.6 Raw Class TODO 2.7 Priming The only way to prime records is through the prime method on DatabaseService, which takes a sequence of records, the field to be primed on those records, and the model to be primed on that field. It optionally takes a sequence of already known foreign records and a Mongo ReadPreference. For example: val checkins: List[Checkin] =... services.db.prime(checkins, Checkin.venueId, Venue) To access the primed foreign object on field foo, use the foofk method on the record, which takes the model of the foreign object as an argument and returns an Option of the foreign object: 2.4. Other Methods 7

12 spindle Documentation, Release val venues: List[Venue] = checkins.flatmap(_.venueidfk(venue)) (This is somewhat clunky, mostly because of having to pass around the model of the foreign object (in this case, Venue) everywhere. This is necessary in order to decouple foreign key fields from the models they point to and so avoid dependency hairballs.) 2.8 Proxies TODO 2.9 Reflection TODO 2.10 Field Descriptors TODO 8 Chapter 2. Records

13 CHAPTER 3 Custom Types In addition to all of the standard Thrift types, Spindle codegen makes available a few extras. 3.1 Enhanced Types Enhanced types are types tagged with an annotation so as to produce either a custom protocol format or a custom Scala type. Enhanced types are defined with the enhanced_types annotation on a Thrift typedef, along with custom logic in the code generator to deal with the enhanced type. For example: // A BSON ObjectId, stored as a binary blob. typedef binary (enhanced_types="bson:objectid") ObjectId // A UTC datetime, stored as millis since the epoch. typedef i64 (enhanced_types="bson:datetime") DateTime Without the enhanced types mechanism, an ObjectId would be serialized as binary over the wire and represented as a ByteBuffer or an Array[Byte] in Scala code. With the enhanced types mechanism, this will be serialized as binary in the binary protocols (TBinaryProtocol, TCompactProtocol) but receive special handling in TBSONObjectProtocol (using the native ObjectId type) and in TReadableJSONProtocol (using a custom ObjectId encoding). In the Scala code, it will be represented as an instance of ObjectId. 3.2 Bitfields In order to use space more efficiently, sometimes you want to store several boolean values into a single integer (i32) or long (i64) value. Spindle calls these fields bitfields. Bitfields come in two variants, with and without set bits. (With set bits, a single boolean value will take two bits, one to determine whether or not the boolean is set, and another for the boolean value itself.) Spindle has some features to make working with bitfields more convenient. You can associate a i32 or i64 field with a bitfield struct. A bitfield struct is a Thrift struct with only boolean fields. If a field foo is marked with a bitfield_struct or bitfield_struct_no_setbits annotation, then an additional foostruct method will be generated which returns a populated boolean struct. Bitfield annotations are applied directly to a class field (not through a typedef), as follows: struct Checkin { 1: optional i32 flags (bitfield_struct="checkinflags") 9

14 spindle Documentation, Release struct CheckinFlags { 1: optional bool sendtotwitter 2: optional bool sendtofacebook 3: optional bool geocheat In this example, the Checkin struct will have all the normal methods for dealing with flags as an i32, as well as a flagsstruct method that returns an instance of CheckinFlags. 3.3 Type-safe IDs You often use BSON ObjectIds as primary keys in Mongo collections. This means common collectons like Checkin and Venue would use the same type as their primary key. In order to avoid errors (such as passing a List[ObjectId] of checkin IDs to a method expecting a List[ObjectId] of venue IDs), Spindle includes a mechanism for tagging common types so they have distinct type-safe version. This behavior is triggered by using the new_type="true" annotation on a typedef. In Scala code, this will turn the type alias into a tagged type, which means it s a new subtype of the aliased type. For example, CheckinId is a tagged ObjectId (unique subtype of ObjectId). Because it s a subtype, you can use CheckinId anywhere you would expect an ObjectId. In order to use an ObjectId where a CheckinId is required, you will need to cast it. A convenience method (with the same name as the type) will be generated to perform this cast. For example: CheckinId(new ObjectId()). Sample usage, in Thrift (ids.thrift): package com.foursquare.types.gen typedef ObjectId CheckinId (new_type="true") typedef ObjectId VenueId (new_type="true") struct Checkin { 1: optional CheckinId id (wire_name="_id") struct Venue { 1: optional VenueId id (wire_name="_id") And in Scala: import com.foursquare.types.gen.idstypedefs.{checkinid, VenueId // cast a regular ObjectId to CheckinId val checkinid: CheckinId = CheckinId(new ObjectId()) // cast a regular ObjectId to VenueId val venueid: VenueId = VenueId(new ObjectId()) // compile error, this won t work because VenueId and CheckinId are different subtypes of ObjectId val checkinid2: CheckinId = venueid // works, because CheckinId is a subtype of ObjectId and can be automatically upcast val unsafecheckinid: ObjectId = checkinid Note that the tagged types live in an object with the same name as the thrift file with Typedefs appended to the end. 10 Chapter 3. Custom Types

15 CHAPTER 4 Enums Enumerations in Thrift are defined with the enum keyword. Enumeration values have names and integer identifiers. When compiled to Scala code, enumerations are represented by a class (of the same name as the enumeration), a companion object, and objects for each of the enumeration values (defined inside the companion object). 4.1 Enum value methods The following methods are available on each value of an enumeration: id - integer id of the enum value name - string name of the enum value, as represented in Thrift source (not intended to be stable) stringvalue - string value of the enum value, as represented by string_value annotation in Thrift (intended to be stable); if there is no annotation, the name is used compare - compare two enum values by their ids meta - access the companion object for the enum 4.2 Companion object methods The following methods are availabel on an enumeration s companion object: findbyid - given an integer id, return an Option of the enum value with that id, or None findbyidornull - given an integer id, return the enum value with that id, or null findbyname - given a string name, return an Option of the enum value with that name, or None findbynameornull - given a string name, return the enum value with that name, or null findbystringvalue - given an string value, return an Option of the enum value with that string value, or None findbystringvalueornull - given an string value, return the enum value with that string value, or null unapply - alias for findbyname (TODO: should be findbystringvalue) 11

16 spindle Documentation, Release Examples Example thrift: enum ClientType { android = 1 blackberry = 2 iphone = 3 web = 4 unknown = 5 Example Scala: val client: ClientType = ClientType.web 12 Chapter 4. Enums

17 CHAPTER 5 Working with Mongo 5.1 Annotations In order to use Spindle structs with Mongo, they must have the required Mongo annotations. mongo_collection - name of the Mongo collection mongo_identifier - name of the Mongo instance There are also a number of optional Mongo annotations: primary_key - the name of the primary key field foreign_key - one or more annotations with names of foreign key fields index - one or more annotations with indexed fields Example: struct Checkin { 1: optional ids.checkinid id (wire_name="_id") 2: optional ids.userid userid (wire_name="uid") 2: optional ids.venueid venueid (wire_name="venueid") (primary_key="id", foreign_key="userid", foreign_key="venueid", index="userid: asc", index="venueid: asc", mongo_collection="checkins", mongo_identifier="foursquare") 5.2 Rogue Queries There are two main differences between Lift Record and Spindle when it comes to creating and executing Rogue queries. First, queries are not created by calling Rogue methods on a model. Queries must be created explicitly by wrapping a model in a SpindleQuery (which we recommend aliasing to Q). Second, queries are not executed by called an execution method on the query, the query must be sent to a SpindleDatabaseService object to execute it. For example: 13

18 spindle Documentation, Release import com.foursquare.rogue.spindle.{spindlequery => Q import com.foursquare.rogue.spindle.spindlerogue._ val q = Q(Checkin).where(_.userId eqs 646).and(_.photoCount > 0) val checkins = db.fetch(q) Here is a basic SpindleDatabaseService implementation: import com.foursquare.rogue.spindle.{spindledbcollectionfactory, SpindleDatabaseService import com.foursquare.spindle.untypedmetarecord import com.mongodb.{db, Mongo, MongoClient, MongoURI object db extends SpindleDatabaseService(ConcreteDBCollectionFactory) object ConcreteDBCollectionFactory extends SpindleDBCollectionFactory { lazy val db: DB = { val mongourl = System.getenv("MONGOHQ_URL") if (mongourl == null) { // For local testing new MongoClient("localhost", 27017).getDB("mydatabase") else { // Connect using the MongoHQ connection string val mongouri = new MongoURI(mongoUrl) val mongo = mongouri.connectdb if (mongouri.getusername!= null && mongouri.getusername.nonempty) { mongo.authenticate(mongouri.getusername, mongouri.getpassword) mongo override def getprimarydb(meta: UntypedMetaRecord) = db override def indexcache = None 14 Chapter 5. Working with Mongo

19 CHAPTER 6 Indices and tables genindex modindex search 15